Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for performing HARQ in a carrier aggregation system.
Discussion of the Related Art
A carrier aggregation system has recently drawn attention. The carrier aggregation system implies a system that configures a broadband by aggregating one or more component carriers (CCs) having a bandwidth smaller than that of a target broadband when the wireless communication system intends to support the broadband. In the carrier aggregation system, a term, serving cell, is also used instead of the CC. Herein, the serving cell consists of a pair of downlink component carrier (DL CC) and uplink component carrier (UL CC), or consists of only the DL CC. That is, the carrier aggregation system is a system in which a plurality of serving cells is assigned to one user equipment.
Conventionally, in the carrier aggregation system, it is considered to aggregate only CC of the same mode. That is, it is considered to aggregate the CCs that operate in the frequency division duplex (FDD) mode or to aggregate the CCs that operate in the time division duplex (TDD) mode. Particularly, in case of the TDD, it is assumed that the CCs which are aggregated use the same uplink-downlink (UL-DL) configuration. The UL-DL configuration is to notify which one is used either uplink (UL) or downlink (DL) for the respective subframes within the frame that is made up of multiple subframes.
However, in the future wireless communication system, it may not be required to confine the above considerations. For example, the carrier which is comprised of only DL subframes may be aggregated to the carrier that operates as the TDD.
In such a case, the method of performing hybrid automatic repeat request (HARQ) on the premise of aggregating carriers of the same way is required to be changed. That is, the timing between scheduling information and the data scheduled, the timing between acknowledgement/not-acknowledgement (ACK/NACK) for the data, and the like are required to be changed.